View original topic: Gas mixing in oil
tdoman Sun Aug 02, 2020 1:40 pm

I have a 1600 cc engine on my dune buggy with a weber progressive carb. I noticed that gas is getting into the oil. It's causing bad oil leaks and oil pressure gauge to read abnormally high pressure when revving engine.

Does anyone have ideas what might be causing this?

I recently switched to a low pressure electric fuel pump that could be the cause but it's done it before when I used my stock fuel pump. I'm wondering if some sand got into the carb causing something to not work right. The engine runs and sounds fine when accelerating.

andk5591 Sun Aug 02, 2020 2:40 pm

Gas in oil is bad. You are thinning the oil out and can damage things. Usula causes are bad emchanical pump, but you have electric. You should be running around 2 or so PSI pressure. Stuck needle valve or float can cause this.

Fix it now.

tdoman Sun Aug 02, 2020 4:05 pm

Ya, that makes sense. How do you prevent it from getting stuck?...besides not driving on the sand. :)

I've got a sand cover for the carb air filter to stop sand from getting into the carb. Is there anything else I can do besides that?

Wulfthang Sun Aug 02, 2020 9:59 pm

The only way that gasoline could get into the oil thru the carb without running very super rich, is if it's free flowing while it's sitting parked. Then it would run in and seep past the piston rings into the crank case. Is your fuel tank sitting above the carb?

If it was running in while the engine was running, it wouldn't have the chance to seep past the rings before it was burned and blown out the exhaust. It would be running very rich. If it was so rich that excess was seeping past the rings, it would be running so rich that it would have trouble running. It would have to be a flooding scenario.

Once you fix it, you need to change the oil and filter and take it for a nice long run to get it hot enough to vaporize and fuel still in the crank case.

earthquake Sun Aug 02, 2020 10:30 pm

Could be a pin hole in the fuel pump diaphragm.


tdoman Sun Aug 02, 2020 10:35 pm

yes, the tank is above the carb and is likely free flowing while parked/off. I have a shutoff value for the gas line so I should probably start shutting off the gas line when it's not running and that would stop it.

dirtkeeper Mon Aug 03, 2020 7:07 am

Did you change the oil when you changed the fuel pump? Maybe it has gas In the oil from the previous possible bad fuel pump. And everything is ok now.

tdoman Mon Aug 03, 2020 7:56 am

Yes, I changed the oil and will clean the carb. Then I'll monitor it to make sure it isn't happening again.

Wulfthang Mon Aug 03, 2020 8:29 am

It is possible that a grain of dust got past the air cleaner and then found it's way thru the passages in the carb to finally end up in the fuel needle valve but if so, you need to buy a lottery ticket!! Most likely, if the needle valve is sticking it's because some crud got past the fuel filter and dingered it.

I have seen needle valves damaged (by a grain of dust) just enough to not seal right anymore. Try replacing the needle valve and then install two new fuel filters one behind the other.

L5wolvesf Mon Aug 03, 2020 1:28 pm

Several questions given the info supplied so far:
Why was an electric pump installed?
What psi is the pump set/regulated at? Webers do not like pressure over 2.5 psi.

Has the carb ever been tuned and / or rebuilt?

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